Re: mercury 150hp 1980.(lack of power when engine under strain)
Enough with the throwing parts at it routine. It's ineffective and can be expensive, not to mention accidentally installing more problems.
You can test the rectifier, go or no-go with an ohmmeter. The procedure is in a FAQ on this web site.
Stator outputs are measured with a DVA (Direct Voltage Adapter) meter, which is a peak voltage integrator followed by a DC meter, usually in one device. Peak voltage is significant. RMS, as measured by the average meter means nothing in the diagnostics. Readings are in the factory manual, and are available at CDI's web site.
For now, with an ordinary AC voltmeter, you can disconnect the 2 yellow wires to the rectifier. Across those wires you should measure approximately 15V per 1000 rpm of engine speed.
The voltage problem may be just a wire broken under the insulation near a crimped connector. That same break would cause most Mercury rectifiers to short out as soon as the engine is sped up above idle.
If the ignition system is barely firing, the extra load of a shorted rectifier could lower the output of the charge coils (connected to the ignition) enough to cause misfire. If the ignition is in good shape, the slightly diminished output of the charge coils would not make a difference.